10 month 26 day, People's Daily page 7 published the investigation "Say No to the 'Scam Targeting the Elderly' of Water Purifiers." In the report, Mr. Zhang from Hohhot, Inner Mongolia, described this scene: the door-to-door staff member "inserted an electrolysis rod into clear tap water, and the transparent liquid instantly churned out rust-colored foam," then said: "Look! How dirty your tap water is!" That water purifier advertised as "free," plus the filters and other accessories that had to be purchased, ended up costing 5400 yuan.
Our judgment is simple: this experiment cannot prove the water is dirty. It proves only one thing, that water can conduct electricity.
1. What actually happens in the experiment
The "electrolysis rod" in the salesperson's hand is actually an electrified device with two metal electrodes at the front end. When it is inserted into water and powered on, current flows from one electrode through the water to the other electrode.
The key point is: for current to flow through, the water must contain ions that can conduct electricity. Tap water and mineral water contain dissolved minerals such as calcium, magnesium, sodium, bicarbonate and chloride ions, and these make the water able to conduct electricity. Once powered on, the metal electrode serving as the positive pole (iron is commonly used in such demonstrators) is dissolved out by electrolysis and enters the water, then reacts with the water to form yellow-brown and dark-green hydroxide flocs, which look like "rust" and "dirt."
So that cup of "dirty stuff" mainly comes from the electrode itself, not from pollutants originally present in the water.
Now look at the comparison salespeople love to demonstrate: when water filtered by a water purifier is electrolyzed, it barely changes color. The reason is the same: water purification processes such as reverse osmosis (RO) remove most of the dissolved ions from the water, so the water barely conducts electricity, and naturally the electrode cannot "dissolve" anything out.
This leads to a somewhat ironic conclusion: according to the logic of this experiment, the richer the minerals in the water, the "dirtier" it looks. A qualified bottle of natural mineral water may look even more "frightening" when electrolyzed than tap water. Different demonstrators use different electrode materials, and the precipitate may also be white or other colors, but the principle is the same and has nothing to do with whether the water is clean.
2. Why this trick works especially well on older people
Because it is intuitive enough. A glass of clear water turns into "rusty water" within seconds, creating a strong visual impact, and ordinary people find it hard to rebut the electrochemical principle behind it on the spot.
The People's Daily report provided data on how common this type of scam is: according to statistics from the national consumers association smart 315 platform, in the 2026 months before 7, the number of water purifier complaints had already exceeded the full-year level of 2024; in the single month of 7 alone, the number of complaints increased by 40.17% compared with 1, showing a month-by-month upward trend throughout the year. In several cases in the report, an elderly person spent 2980 yuan on a water purifier, while the public price of the same model on mainstream e-commerce platforms was only five or six hundred yuan.
Liu Junhai, a professor at the Renmin University of China Law School, said in the report: "Scientific experiments should reveal the truth, not become marketing props that conceal the truth and mislead consumers." He also reminded: "Whether water quality is safe should be based on national standards and scientific test results; consumers should not make misjudgments because of experiments with strong visual impact."
III. What to look at scientifically when judging whether water is good
Since the electrolysis experiment is unreliable, what is reliable?
1. First, look at national standards and official reports. In China, the basis for domestic drinking water is GB 5749-2022, the Standards for Drinking Water Quality, which covers 97 indicators including microorganisms, disinfectants, inorganic substances, organic substances and sensory characteristics. Water supply companies in many cities regularly disclose the test results of treated water and distribution network water, which can be found on the official websites and WeChat public accounts of local water affairs departments or water supply companies.
2. Different problems should be judged by different indicators. Whether water is good cannot be answered by a single indicator:
- Worried about organic pollution: look at organic indicators such as oxygen consumption (permanganate index) and total organic carbon;
- Water is turbid or has sediment: look at turbidity;
- Whether disinfection is sufficient: look at residual chlorine;
- Heavy scaling when boiling water: look at total hardness;
- Worried about bacteria or heavy metals: the only option is to send a sample to a qualified testing institution and test it using laboratory methods.
3. High total dissolved solids (TDS) does not mean the water is dirty. TDS mainly reflects how many minerals are dissolved in the water. The national standard limit for TDS is 1000 mg/L, and most urban tap water is far below this figure. Elevated TDS mainly affects taste and scaling, and cannot be used on its own to judge whether water is safe.
4. If you really have doubts, send it for testing. If your home is in an old residential community, uses secondary water supply, or uses well water, the most reliable approach is to commission a third-party testing institution with CMA qualification to test according to national standard methods. This is more credible than any on-site demonstration.
IV. Three sentences to teach parents to see through scams
This section can be screenshotted and forwarded to the elders in the family:
- "Free water testing, color changes on the spot" — first ask the person to leave. Legitimate testing will not use an electrolysis rod to give a conclusion in a few seconds.
- Anyone who says a water purifier can "cure diseases," "fight cancer" or "lower the three highs" is engaging in false advertising. The China Consumers Association has clearly reminded consumers that the core function of a water purifier is to improve drinking water quality and that it has no disease-treatment effect whatsoever.
- If you really want to buy one, go to legitimate channels and read the nameplate clearly before paying. A legitimate water purifier should be labeled with information such as rated total net water volume, water efficiency grade, wastewater ratio, and filter life. Before buying, check the price of the same model on a legitimate e-commerce platform.
If you have already been scammed, remember to keep the promotional materials, transfer records, invoices and receipts, and communication records, and promptly complain to a consumers association or call 12315.
V. If you really want to understand your own water
Checking reports and sending samples for testing are the right way to judge whether water is drinkable. In daily life, if you want to know whether the water purifier is working, whether there is any change before and after replacing the filter, or what differences there are between different water sources, you can also use portable quick-test tools, testing at fixed times and with fixed methods, to observe trends and make comparisons.
The Water Detective under AtomBit that we make is one such tool. It uses spectroscopy and electrode methods to read indicators such as organic matter, turbidity and TDS in just a few seconds. But we also need to be clear about what it cannot do: it cannot test for bacteria, heavy metals or pH, and no matter how good the readings look, they cannot prove the water is safe to drink. Whether drinking water is safe is subject to the report of the local water authority or third-party testing.
We have always hoped to make water quality understandable to everyone. Once you understand it, you are less likely to be frightened by a glass of “discolored water.”
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About Us
Shenzhen AtomBit Technology Co., Ltd. focuses on micro-spectral sensing and intelligent water quality testing, with products covering water quality sensor chips, online monitoring sensors and portable testing terminals. AtomBit is a drafting unit of two association standards: the Technical Guidelines for Online Water Quality Monitoring Systems Using Spectroscopy (T/CWEC 13-2019) and the Technical Specification for Intelligent Modules for Online Water Quality Monitoring at the End of Urban Water Supply Networks (T/CAQI 93-2019).
Reference: People's Daily, 2026, 10 26, page 7, “Say No to Water Purifier Scams Targeting the Elderly”; GB 5749-2022, Standards for Drinking Water Quality.